Conventionally, a method such as described below has been generally employed to display image information on the display panel of a display device. Initially, an external device (image information processing device) transmits desired image information and like information in the form of video signals to a display device through wire. The video signals thus transmitted are inputted to a driver circuit (driver LSI) configured to drive pixels included in the display panel of the display device via input signal lines. In turn, the driver circuit drives the pixels according to the video signals thus inputted, thereby displaying the image information on the display panel.
In recent years, such a display device as an electrophoretic display for example has been under research and development for use as a paper-like thin flexible display or electronic paper. A display device with higher definition and higher resolution than conventional liquid display devices or like conventional devices is needed to realize a flexible display of high display grade. To this end, a display device of, for example, active-matrix or passive-matrix type having a very large number of pixels and display electrodes or signal lines is needed. Such a display device has a larger number of semiconductor chips as driver circuits connected to signal lines or scanning lines than a conventional one.
In order to realize the aforementioned high-definition and high-resolution display, about 3000×(4-8 bits) lines are required as the total number of input signal lines connected to the driver circuits for video signals for each of the colors, R (red), G (green) and B (blue) for example. In this case, if, for example, 100 chips are mounted as the driver circuits, the number of input signal lines connected to each driver chip is 30×(4-8 bits)×(R, G and B). Thus, a large number of input signal lines are required for each driver circuit. For this reason, it becomes very difficult to mount and handle individual driver circuits, which raises a large problem that mounting and routing for a whole display device becomes complicated and stiffened.
As the display definition has been rendered high in recent years, the number of output pins is increased to reduce the number of input lines for the purpose of avoiding such a mounting problem, which results in a driver LSI having an increased chip size. An LSI chip can be mounted directly on glass by COG or a like technique. However, if a large chip is used in a flexible display employing a plastic substrate or a like substrate, such a problem is likely that an LSI is broken or a mounting portion is undone.
To avoid complicated routing, video signals are preferably inputted wirelessly rather than through wire. The flexible display, in particular, has to meet the requirement that the display be able to be handled like paper while being conveniently rewritable. For this reason, wireless input of video signals to the flexible display is preferable.
Heretofore, a display device wherein an antenna, receiving circuit, driver circuit, display panel and power source are disposed separately from each other and connected to each other, has been proposed as a display device capable of displaying image information based on video signals wirelessly transmitted to the display device from an external device physically separated from the display device (see, for example, patent literature 1: Japanese Patent Laid-Open Publication No. HEI 5-202358 (pp. 24-25 (0071) and FIGS. 2 and 3). As an example of a display device thus configured, there has been developed for actual use an active-matrix type liquid crystal display device in which plural driver circuits each having multiple input signal lines are disposed behind an antenna/receiving circuit for wireless input from an external device.
FIG. 10 is a conceptual diagram illustrating the configuration of a conventional wireless input display device. In FIG. 10, an external device (not shown) transmits video signals to display device 80. The video signal thus transmitted are received by antenna 81 and receiving portion 82 and then outputted from the receiving portion 82 to driver circuit 84 through input signal lines 83. The driver circuit 84 drives pixels of display panel 85 according to the video signals received. A separately-provided power source portion 86 supplies electric power to different pieces of hardware through power output cable 87 (see patent literature 1).
The display panel 85 has an array substrate formed with, for example, TFTs (switching elements), pixel electrodes, interconnections and the like, and a color filter substrate formed with common electrodes. As described above, color display of image information can be realized by driving the pixels of the display panel 85 with the driver circuit 84.
The configuration of driver circuit 84 will be described below in detail.
FIG. 11 is a conceptual diagram illustrating the configuration of a conventional driver circuit. Like reference characters are used to designate like or corresponding parts throughout FIGS. 11 and 10. As shown in FIG. 11, the driver circuit 84, which is a driver LSI associated with source signal lines of an active-matrix type display panel, comprises a timing generator circuit 88, a sample hold circuit 89, and an output buffer circuit 90, which are electrically interconnected.
RGB video signals are inputted to the driver circuit 84 via input signal lines 83a. The sample hold circuit 89 samples RGB video signals inputted within one horizontal scanning period sequentially based on sampling clock signals generated from the timing generator circuit 88. After having been sampled for one horizontal scanning period, the RGB video signals are amplified by the output buffer circuit 90 and then outputted to the signal lines (source lines) on the display panel 85 shown in FIG. 10. On the other hand, the power source portion 86 shown in FIG. 10 supplies the driver circuit 84 with source voltage. Though not shown, a scanning driver circuit (gate driver LSI) outputs horizontal scanning signals to scanning lines (gate lines) on the display panel 85.
In order for such a conventional display device to realize high-definition and high-resolution display comparable to that realized based on wired input of video signals as described above, it is required that the receiving portion 82 be provided with routing of a total number of 3000×(4-8 bits)×(R, G and B) input signal lines 83 and, at the same time, about 100 driver circuit chips 84 each having a number of input signal lines 83a as large as 30×(4-8 bits)×(R, G and B) be mounted.
However, it is very difficult to mount and handle these driver circuits 84 individually and, hence, routing for the whole display device 80 is complicated and stiffened. That is, the same problem as with wired input arises even with wireless input. Also, the display device according to patent literature 1 calls for a very high speed receiving circuit LSI for handling high-frequency signals in realizing high-definition and high-resolution display of high display grade based on wireless input. In this case, a large electric power becomes necessary, which raises another problem that a high-capacity power source is needed.
For the reasons stated above, a high-definition and high-resolution display device such as a flexible display is desired to have a driver circuit requiring as simple routing as possible and to be operable at a low electric power, whether through wire or wirelessly the input of image information is made.
Another proposed conventional art is a portable electronic device having a display portion capable of displaying image information obtained in a non-contact manner. For example, patent literature 2 (Japanese Patent Laid-Open Publication No. 2001-344578 (FIGS. 1,2,9,10 and 11)) has proposed a portable electronic device including a combination of a non-contact IC card and a display device, wherein a wireless input/receive portion comprising an antenna part and an RF part, an IC card chip portion having a microprocessor and a power source part configured to obtain electric power from received signals, a CPU including a display driver circuit, and a display device are interconnected and separately disposed. Such a portable electronic device is configured to obtain electric power from signals received by wireless input and hence is capable of realizing wireless transmission and receipt of data and display of data on the IC card side.
However, even the portable electronic device according to patent literature 2 needs to be mounted with multiple driver circuits each having a large number of input signal lines for realizing high-definition and high-resolution display because the positional relation between the wireless input/receive portion, driver circuits and the display device is the same as in the aforementioned patent literature 1. In order to obtain electric power from data signals inputted wirelessly, the portable electronic device according to patent literature 2 is configured to receive signals at only one wireless input portion to turn the signals into electric power. Therefore, it is practically difficult for such a portable electronic device to have a high-capacity power source part adapted to wireless input for driving a high-definition and high-resolution display device.
As described above, the wireless input portion, receiving portion, display driver circuit and display panel are interconnected and separately disposed according to any one of the patent literature 1 and patent literature 2. In order to realize a high-resolution flexible display of high print grade by utilizing these conventional techniques, driver circuits each having a large number of input signal lines need be disposed and mounted in a larger number than ever. In such a case where each driver circuit has a large number of input signal lines, there arises a problem that mounting and handling of such driver circuits becomes very difficult.
In the case of the flexible display, an LSI circuit capable of high-speed receiving operation is needed for wireless input of video signals because the flexible display is of high resolution. Accordingly, the required electric power is increased, which raises a problem that a high-capacity power source becomes necessary.